Relaxant effect of rat PHI, PHI-Gly and PHV(1-42) in the rat gastric fundus

A new endogenous form of PYY isolated from canine ileum: Gly-extended PYY(1-36)

We purified and identified the peptide YY (PYY) forms present and determined their levels from a portion of the canine ileum directly adjacent to the cecum by a new extraction method designed to prevent and evaluate degradation of endogenous peptides. We used three reverse phase chromatography steps with radioimmunoassay of fractions for PYY-like-immunoreactivity (PYY-LI). The purified fractions underwent intact protein/peptide mass spectrometry identification and sequencing (i.e. "top-down" MS analysis). This analysis confirmed the identity of a new form of PYY, PYY(1-36)-Gly, which co-elutes with PYY(1-36)-NH(2) through all three of separation steps used. The PYY(1-36)-Gly form represents approximately 20% of the total PYY found in this region of the canine intestine. In addition, we also found that the PYY(3-36)-NH(2) form represents 6% of the total PYY in the canine ileo-cecal junction. The physiological implication of the Gly-extended form of PYY(1-36) warrants further investigation.

COOH-terminally extended secretins are potent stimulants of pancreatic secretion

Posttranslational processing of preprosecretin generates several COOH-terminally extended forms of secretin and alpha-carboxyl amidated secretin. We used synthetic canine secretin analogs with COOH-terminal -amide, -Gly, or -Gly-Lys-Arg to examine the effects of COOH-terminal extensions of secretin on bioactivity and detection in RIA. Synthetic products were purified by reverse-phase and ion-exchange HPLC and characterized by reverse-phase isocratic HPLC and amino acid, sequence, and mass spectral analyses. Secretin and secretin-Gly were noted to coelute during reverse-phase HPLC. In RIA using eight different antisera raised against amidated secretin, COOH-terminally extended secretins had little or no cross-reactivity. Bioactivity was assessed by measuring pancreatic responses in anesthetized rats. Amidated canine and porcine secretins were equipotent. Secretin-Gly and secretin-Gly-Lys-Arg had potencies of 81 +/- 9% (P > 0.05) and 176 +/- 13% (P < 0.01), respectively, compared with amidated secretin, and the response to secretin-Gly-Lys-Arg lasted significantly longer. These data demonstrate that 1) amidated secretin and secretin-Gly are not separable under some chromatographic conditions, 2) current RIA may not detect bioactive COOH-terminally extended forms of secretin in tissue extracts or blood, and 3) the secretin receptor mediating stimulation of pancreatic secretion recognizes both amidated and COOH-terminally extended secretins.

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

Non-adrenergic non-cholinergic relaxation of the rat stomach

1. Receptive and adaptive relaxations of the proximal third of the stomach are reflex responses that enable the stomach to accommodate large volumes with minimal increases in intraluminal pressure. The smooth muscle relaxations are termed non-adrenergic non-cholinergic (NANC). 2. Nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) are considered to be the principal neurotransmitters of NANC relaxation of the rat stomach. NO appears to be mainly responsible for the speed of the relaxation and VIP appears to be responsible for the duration. 3. Studies indicate that inhibitory neurons may also release other neurotransmitters, such as adenosine triphosphate (ATP) and peptide histidine isoleucine (PHI). 4. NANC relaxation of the rat stomach is a complex phenomenon that appears to involve many neurotransmitters, each with a specific role.

Influence of selective VIP receptor agonists in the rat gastric fundus

The receptor subtypes involved in the relaxant effect of vasoactive intestinal polypeptide (VIP) in the rat gastric fundus were investigated in vitro. The selective VIP2 receptor agonist [Ac-H1,E8,K12,Nle17,A19,D25,L26,K27,28,G29,30,++ +T31]VIP(cyclo21-25) (RO25-1553) induced a concentration-dependent relaxation (EC50 2.8 nM), while the selective VIP1 receptor agonist derived from growth hormone-releasing factor (GRF) [K15,R16,L27]VIP-(1-7)/GRF-(8-27) had no effect up to 1 microM. [R16] chicken secretin, a selective VIP1 receptor agonist, induced relaxation with a potency of 4.8 nM but its maximal effect was clearly lower than that of VIP, pituitary adenylate cyclase-activating peptide [PACAP-(1-27)] and RO25-1553. This effect was reproduced by porcine secretin (EC50 2.1 nM). It is concluded that the rat gastric fundus contains functional VIP2 receptors but not VIP1 receptors, and that specific secretin receptors are also present.

Peptide histidine isoleucine-like immunoreactivity release from the rat gastric fundus

1. Longitudinal muscle strips from the rat gastric fundus were subjected to in vitro electrical field stimulation (EFS) under non-adrenergic non-cholinergic (NANC) conditions to study the release of peptide histidine isoleucine-like immunoreactivity (PHI-LI) and the correlation between PHI-LI release and NANC relaxation. 2. Different radioimmunoassay (RIA) systems employing C-terminal- and N-terminal-specific anti-PHI sera were used to determine the relative contributions of PHI and its C-terminally extended forms, peptide histidine glycine (PHI-Gly) and peptide histidine valine [PHV(1-42)], to the PHI-LI released by the rat gastric fundus. 3. In the presence of atropine (1 microM) and guanethidine (5 microM), EFS (120 mA, 1 ms, 0.25-32.0 Hz, trains of 2 min) induced frequency-dependent relaxations of 5-hydroxytryptamine (3 microM) pre-contracted strips. 4. EFS at frequencies of 8-32 Hz evoked significant increases in PHI-LI outflow. The increases in PHI-LI outflow evoked by 16-Hz EFS were abolished by tetrodotoxin (3 microM) and by a calcium-free medium, indicating an active release process from intramural nerves. 5. The EFS-induced release of PHI-LI measured with the N-terminal-specific antiserum was significantly greater than that detected with the C-terminal-specific antisera. 6. Sephadex G-25 gel permeation chromatographic analysis was performed on the PHI-LI release in response to 32-Hz EFS. A C-terminal-specific antiserum revealed one peak co-eluting with the rat PHI standard. When PHI-LI was measured with the N-terminal-specific antiserum, two peaks were found that co-eluted with the rat PHV(1-42) and rat PHI-Gly/PHI standards, respectively. 7. The present data suggest that the extended forms of PHI are the primary components of the PHI-LI released by NANC inhibitory neurones in the rat gastric fundus and support a NANC inhibitory neurotransmitter role for PHI and its extended forms in this tissue.

Concentrations and distribution of vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI) and peptide histidine valine (PHV) in the cerebral cortex and the suprachiasmatic nucleus of the mouse

Prepro-vasoactive intestinal peptide (prepro-VIP) is processed to at least three biologically active peptides: VIP, peptide histidine isoleucine (PHI) and an extended PHI, peptide histidine valine (PHV). The aim of the present investigation was by chromatography combined with RIA and immunocytochemistry to determine which of these peptides were present in the cerebral cortex and the hypothalamic suprachiasmatic nucleus (SCN) of the mouse. These regions were chosen since they are known to contain a high concentration of VIP but the relative concentration of PHI and PHV is not known. Tissue was extracted and subjected to gel chromatography and high-pressure liquid chromatography (HPLC). VIP and PHI immunoreactivities co-eluted with synthetic rat VIP and PHI. A minor peak of PHI and prepro-VIP(111-122) immunoreactivities eluted at the position of synthetic PHV. Surprisingly, a major peak of prepro-VIP(111-122) immunoreactivity eluted in a position not related to any other immunoreactivity indicating the presence of prepro-VIP(111-122). Measurements of these immunoreactivities in cortical and suprachiasmatic extracts revealed that VIP was found in the highest concentration whereas PHV was found in the lowest. Immunoreactivity for PHI and prepro-VIP(111-122) was found in moderate concentrations. Except for prepro-VIP(111-122) which was found to be approximately 3 x higher concentrated in the SCN than in the cerebral cortex, the other immunoreactivities were found in almost similar relative concentrations in the two tissues. Using immunocytochemistry, elongated neurons mostly of the bipolar type with prominent processes observed in the cerebral cortex reacted with all antisera tested. More PHI/PHV/prepro-VIP(111-122)- than VIP-immunoreactive (ir) nerve fibers were found in the cerebral cortex. In the SCN, the density of immunoreactivity was the same whatever antiserum used. VIP-, PHI- and prepro-VIP(111-122)/PHV-ir neurons were observed in the ventral part of the nucleus with numerous axons coursing caudodorsally into the subparaventricular area. A substantial number of terminals was detected caudal to the paraventricular nucleus. Minor projections spread to the medial part of the anterior nucleus and to the medial preoptic area hypothalamic. These data show that VIP and PHI are the major active peptides derived from prepro-VIP in the mouse cerebral cortex and SCN whereas PHV was found in minor concentrations. Prepro-VIP(111-122), which so far has been found to have no functional significance, is, therefore, most likely a vaste fragment of processing of PHI in central neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

The presence of nerve fibers immunoreactive for vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), and preproVIP(111-122) in the mouse pineal gland

A low to moderate number of vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI)-immunoreactive nerve fibers with prominent boutons-en-passage were demonstrated in the pineal gland of the mouse. The two peptides, which are parts of the same precursor molecule, were distributed identically in the gland. Positive fibers were present in the connective tissue septae in the gland, in the pineal capsule, and in the pineal parenchyma. No VIP-PHI-immunoreactive elements were found in the deep pineal gland, in the pineal stalk, or in habenular and posterior commissures. This morphological distribution of immunoreactive nerve fibers, which is similar to the distribution in other mammals, indicates that the VIP/PHI fibers of the mouse pineal gland originate exclusively from perikarya in a peripheral ganglion, presumably one of the cholinergic ganglia of the head. No evidence for a VIPergic central innervation was found. VIP and PHI are connected via a bridging peptide equivalent to amino acids 111-122 of the precursor (preproVIP(111-122)). In order to demonstrate the possible existence of this peptide in intra-pineal nerve fibers, antisera directed against a synthetic sequence identical to preproVIP(111-122) and immunohistochemistry were applied. PreproVIP(111-122)-immunoreactive nerve fibers were observed in the mouse pineal gland, with the same distribution pattern and morphology as those immunoreactive for VIP and PHI. To quantify the peptide-immunoreactivities, 50 mice pineals were pooled, extracted, and the concentrations were measured radioimmunologically. The concentrations of the VIP and preproVIP(111-122) immunoreactivities were 1.7 and 2.0 pmol/g, respectively, whereas the concentration of PHI was 0.9 pmol/g.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of peptide histidine isoleucine on pancreatic exocrine secretion in anaesthetized dogs

1. The effects of peptide histidine isoleucine (PHI) on pancreatic exocrine secretion were investigated in preparations of the isolated and blood-perfused dog pancreas as compared with those of vasoactive intestinal peptide (VIP), secretin and glucagon. 2. Each peptide tested was injected intra-arterially (i.a.) as a single bolus. Graded doses of PHI (3-300 nmol/kg), VIP (1-100 nmol/kg) and secretin (0.01-0.3 nmol/kg) caused dose-dependent increases in the secretion of pancreatic juice and bicarbonate outputs, but had little effect on the protein outputs. Glucagon (0.1-10 mumol/kg) produced a bell-shaped dose-response curve for the secretory rate, bicarbonate and protein outputs. 3. The secretory activity of 30 nmol/kg of PHI corresponded roughly to that of 80 pmol/kg of secretin, 9 nmol/kg of VIP and 0.6 mumol/kg of glucagon, respectively. Thus, based on administered dose, PHI was about 375 x less potent than secretin, 3 x less potent than VIP and 20 x more potent than glucagon. 4. The PHI- and VIP-stimulated secretions were inhibited by a VIP antagonist, but not by a glucagon antagonist, SCH23390 (a dopamine D-1 antagonist), L-364718 (a cholecystokinin antagonist) or atropine. 5. Each peptide increased cyclic AMP concentration, but not cyclic GMP concentration, concomitant with the increase in pancreatic secretion. 6. From these results, it is concluded that PHI produces an increase in pancreatic secretion by acting on VIP-preferring receptors on the exocrine pancreatic gland of the dogs. This may be mediated at least in part through the increase of intracellular cyclic AMP concentrations.

Role of nitric oxide and vasoactive intestinal polypeptide in vagally mediated relaxation of the gastric corpus in the anaesthetized ferret

The roles of VIP and NO in vagally mediated relaxations of the gastric corpus were investigated in the anaesthetized ferret. Intracorpus pressure was recorded manometrically during electrical stimulation of the cervical vagus nerve in three groups of animals: one control group (n = 6), one group treated with an inhibitor of NO synthesis (NG-nitro-L-arginine methyl ester (L-NAME), 1.6 mg/kg); and a third group which had been immunized, prior to the experiment, with a VIP-thyroglobulin conjugate (25 nmol equivalent) in Freund's complete adjuvant. In control animals, following treatment with atropine (100 micrograms/kg), vagal stimulation resulted in a frequency dependent fall in intracorpus pressure with the maximum response at 5 Hz of 2.2 +/- 0.3 cm H2O. Two components of the response could be observed: an initial rapid fall over the first 10 s of stimulation followed by a slower decline over the remainder of the stimulation period. In animals treated with L-NAME (n = 6) the initial rapid response was significantly reduced at all frequencies of stimulation (P < 0.05 - P < 0.005, Mann-Whitney U-test) leaving only the slower second component. In immunized animals (n = 6) the initial rapid response to vagal stimulation was not different from control but the slower second component was significantly reduced at 1 Hz (P < 0.005). We conclude that the response to vagal stimulation appears to consist of two components which can be differentiated using L-NAME and autoimmunization to VIP.

Effect of immunisation against vasoactive intestinal polypeptide on gastric corpus tone and motility in the ferret

The role of vasoactive intestinal polypeptide in the control of gastric corpus tone and motility was investigated using auto-antibodies to neutralise endogenous vasoactive intestinal polypeptide. Six ferrets were immunised with vasoactive intestinal polypeptide thyroglobulin conjugate in Freund's complete adjuvant which resulted in a significant increase in plasma vasoactive intestinal polypeptide binding activity compared with unimmunised control animals. In acute experiments the level of spontaneous motility in the period immediately after completion of the surgical preparation was 15 times higher in immunised v control animals (p < 0.02). Surprisingly, however, there was no deficit in the ability of the corpus to accommodate fluid. Peak pressure at the end of a 20 ml ramp distension was not different in immunised animals (5.7 (0.6) cm H2O) compared with controls (4.8 (0.3) cm H2O). It is concluded that the non-adrenergic non-cholinergic inhibitory mechanisms regulating corpus tone and motility are different and that vasoactive intestinal polypeptide acts primarily to regulate phasic contractile activity. Alternatively, because of plasticity in the mechanisms controlling corpus tone, the effect of vasoactive intestinal polypeptide may have been superceded during the timecourse of the immunisation procedure.